Septic System Record Drawings — What Installers, Engineers & County Reviewers Need to See
Introduction
A septic system can be installed perfectly and still miss approval if the record drawing is unclear. Reviewers need to verify component locations, setbacks, and elevations at a glance—without guessing, scaling from fuzzy photos, or requesting a second site visit. Installers and engineers need a repeatable packet that documents the system precisely and addresses the county’s checklist the first time.
This guide outlines what inspectors typically expect on septic as-builts, how installers and engineers can divide responsibilities, and how modern aerial documentation (when used) can make packets clear, defensible, and easy to review. The focus is approvals and accountability—not photography techniques.
The Reviewer’s Shortlist: What Must Be On the Sheet
Most Colorado counties (and many elsewhere) ask for the same core items. Your record drawing should include:
Labeled components: septic tank(s) with inlet/outlet and lid locations, tees/baffles, distribution box, laterals or chambers, cleanouts, pump chamber (if present), vents, inspection ports.
Dimensions & layout: overall field dimensions, lateral spacing and lengths, component-to-component distances.
Setbacks: distances to the home, well, property lines, driveways, drainage features, water bodies, and steep slopes—as required by the permit.
Elevations & slope: invert elevations (in/out of tanks, D-box, pump), finish grade where needed, and slope across the absorption area (and along any pressure line).
Orientation & scale: north arrow, graphic scale bar, and units.
Legend & symbology: a simple legend for symbols and line types.
Coordinate & vertical reference: the coordinate system and vertical datum used (e.g., NAD83 State Plane Colorado North, US foot; NAVD88 (GEOID18)).
Photos: overview photo and 2–3 labeled details (e.g., tank lids, D-box, representative lateral).
Goal: One clean, reviewer-friendly PDF that shows the entire system and allows measurements to be understood without guessing.
Elevations & Slope: What “Defensible” Looks Like
Invert elevations at tank inlet/outlet and D-box outlets are often the make-or-break details. If you measure by rod/laser, state the method succinctly (e.g., “Inverts measured via builder’s level from on-site TBM”).
Slope across the absorption area should be noted when required (e.g., “Field slope 1.0% SW to NE; meets design criteria 0.5–2.0%”).
When aerial data supports elevations: state that heights were checked against ground points or known inverts; include a small accuracy/QA note so the reviewer can trust the numbers.
Setbacks: Make Them Obvious
Draw straight-line dimensions and label them clearly (e.g., “House corner (SW) to D-box: 32.4 ft”).
For property lines or wells that are not visible in the base map, reference a surveyed corner or cite the source of the linework (plat, county GIS)—and label it as such.
If a required setback cannot be directly measured (e.g., obscured well), provide the best available measurement plus a note explaining the reference used.
Common Reasons for Rejection—and How to Avoid Them
Missing inverts
Fix: Add a small elevation table (in/out of tanks, D-box, pump). Note method and datum.
Ambiguous lateral layout
Fix: Show lateral lengths and spacing with simple dimensions; include a legend.
No north arrow/scale
Fix: Always include both; add a graphic scale bar on the sheet.
Unclear setbacks
Fix: Draw and label each setback with a straight dimension; cite reference (house corner, property line).
Mixed units or unknown datum
Fix: State units (US ft) and datum (horizontal + vertical) in the title block; keep decimals consistent.
Oversized, cluttered PDFs
Fix: Optimize imagery, keep one summary sheet, move extra photos to page 2 with captions.
Mini Case: Reviewer Acceptance on First Submittal
An installer flagged four lid locations and the field corners before cover. The designer drafted one sheet with labeled components, setbacks to the house and well, a small invert table, and a north arrow/scale bar. The county received a single PDF and approved without revisions. The packet took less time to prepare than a return site visit—and remains a clean record for future maintenance.
